GEOCHEMICAL CHARACTERISTIC OF THE LOWER SILURIAN OIL SANDSTONES IN WELL ZHONG 1 ZONE, NORTH WESTERN TAZHONG AREA

The lower part of the Lower Silurian sandstones is one of the most important hydrocarbon exploration play in Tarim Basin Based on systematic analysis of the petroleum family composition,various biomarkers and distribution of isotope of petroleum family composition in the saturated fraction from extracts of the Lower Silurian oil sandstones in Well Zhong 1 zone,the results show that the contents of saturated hydrocarbon is from 51.31%～60.15%,the ratio for saturated and aromatics is from 1.68～1.94 in Well Zhong 1,in contrast,the contents of saturated hydrocarbon is 30%,the average ratio for saturated and aromatics is 1,the distribution for n-alkanes is nC₁₂ to nC₃₉ with the major contents of n-alkanes from nC₁₇ to nC₁₉,OEP is from 0.91 to 1.08 in Well Zhong 13. Moreover,the latter is characteristic of a certain content of tricyclic and tetracyclic terpane,C₂₇>C₂₈<29 in consist of steranen and the raising line for isotope of petroleum family composition in the saturated fraction.It therefore can be inferred that the oil for the Lower Silurian oil sandstones is mostly origined from the Middle and Lower Cambrian mixing with a certain of the Upper Ordovician source rocks.